Is it true that our current understanding of physics/aerodynamics don’t explain how these insects can fly? What about frisbees? Is there anything else that defies our present understanding of staying in the air?
No, that’s incorrect.
The Master speaks: Is it aerodynamically impossible for bumblebees to fly?
I’ve only heard this myth about bumblebees, never butterflies.
What’s so mysterious about frisbees? They don’t fly.
If we knew enough to make this thingfly in 1931, and we did, then we certainly know how a bumblebee flies.
I think the “theoretically according to the laws of aerodynamics a bumblebee can’t fly” nonsense was popularized in WWII in order to put down the “ivory tower theorists.” That is perfectly in tune with an anti-intellectual streak in the American credo.
Jimmy Doolittle, among others, flew this plane in closed course races. It was what’s known as “unforgiving” and such races were flown close to the ground. Many fatalities and the GB Super Sportster contributed its share, but not because we didn’t understand how it flew.
But they do glide, in some rather interesting and complex ways. Googling “frisbee aerodynamics” produces lots of links.
The OP implies that frisbees defy our understanding of how things stay in the air. Do any of those sites indicate that?
Jeez, and those things only cost $119, too. Who flew them, little tiny people?
Okay, you’re right. Frisbees do not fly. No need to get all snarky and superior about it. :rolleyes: It’s just another one of those bits of junk information that I’ve got lodged in the gray matter that the aerodynamics of frisbees is not entirely understood. And I thank Unca Cecil for enlightening me about the bumblebee. I gather I’m just totally wrong about the butterfly, huh? They just look very unique in the way they fly, to me.
Oh come now. That wasn’t all that snarky - it was more that I was a bit mystified by where the question came from. You’re being overly sensitive. If I’m really being snarky, you’ll know it. 
The story about bumblebees originated because they have relatively small wings for their weight. Butterflies have very large wings for their weight, so there’s not much problem figuring out how they stay up. Their bouncy, erratic flight, however, may make them more difficult for predators to catch.
Not that I can see. But they do tend to indicate that frisbee flight is by no means trivial.
My post was in response to your statement that frisbees don’t fly. It seems to me that their aerodynamic performance, while certainly not beyond human understanding, is a good deal more involved than that statement would imply.
The insect flight mechanics are not a mistery, there are still things to iron out but there has been an increased interest on the area in the last 10 years or so (mainly research for micro UAVs)
Insects (butterflies, bumblebees, you name it) don´t fly on the same principle as planes, to begin with; the wings move on a figure eight path, seen from the side, more or less “rowing” in the air, the very rapid flapping of their wings cause a relatively large, horizontal vortex on top of the leading edge which by tuning the frequency of the beats can increase lift or perform maneuvres. That vortex (like a tornado, with the air flowing towards the wing tip) is what produces the lift, and at the scale of an insect is much stronger than the lift a plane wing would produce (in fact at that scale the air is so viscous that a plane-like wing would not work properly).
Another factor is the scale of the insects, as you go smaller the wing loading decreases by the cube root of the scale. Imagine you have a plane weighting 1000 kg and with a wing area of 100 sq. m, that gives a wing loading of 10kg per square meter; if you reduce the scale by 1/10, it will weight 10 kg* and the wing area will be 10 sq meters, which gives a wing loading of just 1 kg per square meter. As you can see, as you get smaller you need relatively smaller wings.
As a side note, I´ve built a few ornithopters that work on the same concept and they are a hoot to see flying.
Hmmm, that asterisk up there was meant to point to a foot note explaining why when you reduce an object to 1/10th of it´s size it weights 1/1000th of the original one, that is, the cube root of the scale…
Now that I read that, I made a mistake, wing loading goes down by the square root of the scale, not the cube root.
You mean they do fly? Otherwise my statement is correct.
I shouldn´t post so late in the night…
A plane weighting 1000 kg, reduced to 1/10th scale would weight 1 kg, not 10, so the wing loading should be 0.1 kg per square meter (using the wing area of the first example)… so it´s indeed the cube root of the scale.
Now if you´ll dust off the old dunce cap and sit on a corner.
I´m outta here! 
They do - motion through the air does not need to be self-powered to be considered flight.
-Like a Frisbee in zero-G! 
Then why, in your first post, did you apparently agree with me, by saying “but they do glide?” You were evidently making the same distinction I was, between gliding and true flight. Now you seem to be changing your definition.
Baseballs, stones, and bottles can all fly through the air, in some sense.
The distinction then would be between aerodynamic flight and ballistic flight (stones, bottles, cats, etc…), in the first there´s lift at play.
Frisbees indeed produce lift, try tossing one upside down and see how far it goes; its a glide type flight plus they depend on the spining to remain at the correct flight attitude, so when they loose spin they tumble and fall.
Sorry - it was an attempt to disagree with a respected poster in a mild and civil manner.